COUNT, DISTINCT (unique)

-- Select all
SELECT *
FROM customers;

-- Select some fields
SELECT contact_name, city
FROM customers;

-- Select with computed value
SELECT order_id, shipped_date - order_date
FROM orders;

-- Select unique cities
SELECT DISTINCT city
FROM customers;

-- Count all customers
SELECT COUNT(*)
FROM customers;

-- Count unique countries
SELECT COUNT(DISTINCT country)
FROM customers;